The present invention relates to a linear inductive transducer including electric windings with a primary winding and a pair of secondary windings, a magnetic core, for performing linear displacements relative to the electric windings, a pair of input terminals electrically connected to the primary winding and adapted for being electrically connected to a power supply unit, at least an output terminal electrically connected to the electric windings, the transducer being adapted for providing, through the output terminal, an electric signal indicative of the mutual position between the electric windings and the magnetic core.
The invention also relates to a linear inductive transducer including electric windings with a primary winding and a pair of secondary windings, a magnetic core, for performing linear displacements relative to the electric windings, a pair of input terminals electrically connected to the primary winding and adapted for being electrically connected to a power supply unit, and output terminals electrically connected to the electric windings, the transducer being adapted for providing, through at least one of the output terminals, an electric signal indicative of the mutual position between the electric windings and the magnetic core.
Transducers with these characteristics, in particular of the Linear Variable Differential Transformer (LVDT) type have been known for a long time and utilized, among other things, in many measuring apparatuses for providing electric signals indicative of the mutual position between mechanical parts. These transducers include a primary winding and a pair of secondary windings connected together in series opposition. The windings are wound on a substantially cylindrical bobbin at the interior of which a ferromagnetic core displaces along an axial direction. The primary winding is energized with a sinusoidal voltage and generates, at the ends of the secondary windings, induced voltages that vary as the axial position of the core changes. More specifically, the voltages induced in the secondary windings are equal and oppositely phased when the core is at an axially centered position. Thus, the total voltage at the free terminals of the secondary windings is null at said axially centered position, while its amplitude varies as the axial position of the core changes, and its phase changes in response to the sense of the axial displacement with respect to the centered position.
In U.S. Pat. No. 4,386,467 there is disclosed a possible application of an LVDT in a comparator for checking a hole of a mechanical piece, in which the core and the transducer windings are respectively coupled to two mutually movable arms that carry feelers for touching diametrically opposite points of the hole.
Other types of inductive transducers are known as Half Bridge Transducers or HBT. These transducers include a pair of series connected windings, wound on a bobbin and energized with a sinusoidal voltage at the free ends thereof, and a ferromagnetic core axially movable within the bobbin. The output voltage is drawn at an intermediate point between the windings and its amplitude varies as the axial position of the core changes. The HBTs are broadly utilized in measuring devices, especially in simple devices like axial, or cartridge, heads, in consideration of the attributes of simplicity and inexpensiveness. Furthermore, unlike the LVDT transducers, the half bridge transducers have low output impedance values (e.g., 300 ohm as compared to 2000 ohm that represent a typical value for an LVDT), thus the negative effects due to increased load impedance caused by the cable for the connection to the conditioning units are negligible. In fact, different cable lengths determine different load impedance values at the output of the transducer, and said load impedance in turn determines a variation in the amplitude of the output signal that increases the more the transducer output impedance is higher.
In a half bridge transducer the output impedance is relatively low since it is determined by the parallel of the impedances of the two windings, while it is definitely higher in a differential transformer transducer, where it is determined by the sum of the impedances of the two series connected secondary windings.
Another advantageous feature of the HBT in comparison with the LVDT, particularly in multiple applications in which the signals sent by a plurality of transducers have to be managed, is the possibility of utilizingxe2x80x94between each of the HBT and the conditioning unitxe2x80x94one electric connection wire less (three, as compared to four that are necessary for the differential transformer transducers) thereby simplifying the application.
A drawback of the HBTs is the poor sensitivity, i.e. the low ratio between the detected output signal variation and the associated core displacement. In a half bridge transducer, the sensitivity mainly depends on the geometric characteristics, more specifically on the ratio existing between the dimensions of the windings and those of the core, both generally imposed by the dimensions of the measuring device including the transducer. Hence, it is impossible to independently define the sensitivity and modify it for specific applications, for example in an application of a comparator as the one described in the formerly mentioned patent U.S. Pat. No. 4,386,467. In fact, in this specific case, as there is an xe2x80x9carms ratioxe2x80x9d (i.e., the ratio between the amount of displacement of the feelers and the amount of the associated mutual displacement between the transducer""s core and windings) that is known and generally differs from one, it can be advantageous to define the transducer sensitivity in order to take into account this known ratio, in this way simplifying the processings performed by the conditioning circuit.
An object of the present invention is to provide a linear inductive transducer that overcomes the disadvantages of the known transducers and, more specifically, enables to define its sensitivity regardless of the geometric characteristics, and none the less ensures a lower output impedance value and a lesser number of external electric connections with respect to the known differential transformer transducers.
This and other objects and advantages are achieved by a transducer according to claim 1.
A further object of the invention is to provide a linear inductive transducer that can present the functional charactersitcs of a differential transformer transducer, or a half bridge transducer, or a transducer of another type, by carrying out simple and rapid modifications.
This further object is achieved by a transducer according to claim 8.